Elevator control system



March 16, 1943. P. M. MARTIN ETAL ELEVATOR CONTROL SYSTEM 2 Sheets-Sheet1 Filed Dec. 2, 1941 M 6 a a i i 6M1. v m w w V A 4 w 4 ||.|.l|||.\ IQ.w; w n" w v p D 2 q, w e e y 6 u p a a n w m D lmw Jhw nv w H 4 Z Lv W.(v fl W 1. H w j 5 i D. a

WITNESSES:

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Patented Mar. 16, 1943 2,313,955 Fl C E ELEVATOR CONTROL SYSTEM.

Paul M. Martin, Chicago, Ill., and Alvin 0. Land, East Orange, N. 1.,assignors to Westinghouse Electric Elevator Company, Jersey City, N. 1..

a corporation of Illinois Application December 2, 1941, Serial No.421,306

Our invention relates to electrical control systems of the variablevoltage type and, more particularly, to such systems of this characteras include a regulating means and are sultablefor the operation andcontrol of elevator hoisting motors.

One object of our invention is to provide an electricalcontrol systemwhich shall be inexpensive to construct, install, operate, and maintainin operation.

Another object is to provide an electrical control system which willrequire less engineering time than heretofore necessary on eachindividual installation and which will make it possible to use standardstock control units which may be easily and quickly adjusted or changedwhen installed to suit our particular installation.

A further object is to provide a control system which will so controlthe elevator cars as to increase their riding ease and eliminate anydiscomfort to the passengers.

It is also an object to provide an elevator control system in which thetime for floor-to-floor runs will be held at a minimum.

For a better understanding of our invention, reference may be had to theaccompanying drawings, in which:

Figure 1 is a straight-line diagram of an elevatorcontrol systemembodying our invention; and

Fig. 2 is a key representation of the relays embodied in Fig. 1illustrating their coils and contact members disposed in horizontalalignment with their positions in the straight line circuit so thattheir locations and connections therein may be readily determined.

Our invention is described in connection with a simple elevator system,but it is to be understood that it may be used with much morecomplicated elevator systems or with similar motors used for otherpurposes.

The following relays, switches, etc., are used in the circuit of Fig. l:

A: starting relay for pattern circuit. B: relay for conditioning thesystem for a one-floor run or for a more than onefioor run. U: updirection switch. D: down direction switch. UR=up direction relay.DR=down direction relay.

M=car running relay.

R: car control relay. HSL: high speed inductor relay.

ISL=intermediate speed inductor relay.

SL: stopp'ng inductor relay.

P: sopping inductor control relay. Qzinductor conditioning relay.H=hoisting motor. G: generator. Ex: exciter.

Referring more particularly to Figure 1, we

have illustrated an elevator car Ill as suspended by a cable H whichpasses over a hoisting drum l2 to a counter weight [3. The hoisting drum[2 is fixed upon a shaft H operated by a hoisting motor H. The motor His provided with a field winding HF connected across a pair of supplyconductors L+ and L- which may be supplied with direct current from asuitable source such as an exciter Ex. A spring-operated brake [6controlled by an electromagnetic coil I1 is provided for preventingoperation of the hoisting drum I 2 when the hoisting motor isdeenerglzed.

A variable voltage system of control is provided for operating thehoisting motor H wherein its armature HA is connected in a closedcircuit 9 with the armature GA of a generator G, having a separatelyexcited constant differential field winding GF and a controlled mainfield winding RF. The main field winding provides the ener; gizationforthe generator. The difierential field winding GF is connected to opposethe main field winding RF for purposes of control as will be definedlater. The armature GA of the generator may be driven at a constantspeed by means of any suitable drive motor (not shown).

The direction and speed of the hoisting motor H may be controlled bycontrolling the direction and value of the excitation current for thegenerator main field winding RF. The direction is controlled by an updirection switch U and a down direction switch D. The value of theexcitation current will be controlled as hereinafter described.

The operation of the up and the down direction switches is controlled byan up direction relay UR and a down direction relay DR which, in turn,are controlled by a manually operated switch CS mounted in the car inposition to be controlled by the car attendant when he desires to effectthe starting or stopping of the car.

'A car-running relay M is provided for con ditioning the control systemfor operation when the car is to be moved and also for effecting thereleas of the brake l5 whenthe car is in operation.

Any suitable system may be utilized for automatically decelerating thecar and stopping it level with a floor in response to a stopping operation of the car switch CS. In the present case we have illustrated ahigh speed decelerating inductor relay HSL, an intermediate speeddecelerating inductor relay ISL, and a stopping inductor relay SL. Theserelays may be mounted on the car in position to be operated by suitableinductor plates mounted on the hatchway walls (not shown) at suitabledistances from each floor so that they will operate the relays, whenthey are energized, to decelerate the car from its high speed or fromits intermediate speed, then stop it level with the floor where a stopis being made.

Inasmuch a inductor relay systems for decelerating and stopping elevatorcars are old and well known in the art, no specific illustration of theplates and their location is given. However, if further information isdesired, it may be' obtained in Patent No. 1,884,446, issued October 25,1932, to K. M. White and G. K. Hearn, and assigned to the WestinghouseElectric Elevator Company.

An inductor control relay Q is provided for rendering the inductor relaysystem effective when the car is to make a stop at a floor.

A floor adjusting relay B is provided for conditioning the controlsystem so that the car will make a one-floor run in the most effectivemanner when the car switch CS is thrown to full running position andimmediately returned to its stopping position, and for causing the carto' make a more than one-floor run in the most effective manner when thecar switch is moved to and retained in it car running position.

A relay P, controlled by the intermediate inductor relay ISL and the upand down direction relays is provided for preparing the stoppinginductor relay SL for operation after the relay ISL has operated.

A conditioning relay R, controlled by the car switch CS, is provided forpreventing operation of the relays Q and B, while the car is operated athigh speed until a stop is to be made at a floor.

A starting relay A is provided for preparing the control circuits of thecar for operation when the car is to be started and also for controllingthe use of a pattern circuit or speed controlling system to be describedlater.

In the operation of the variable voltage system and, particularly, whereit is used in connection with an elevator, there are many unlocked-forvariations in the conditions under which the generator and the motoroperate which cause variations in the desired speed of the hoistingmotor.

For instance, there may be unlocked-for changes in the friction of thedriven parts, the resistance value of the windings, changes in load,changes in brush contact which vary the series excitation, etc., whichmay cause the speed of the motor to vary from the speed it should havein response to any selected setting of its controller. In order toovercome these difficulties, we have provided a novel regulating meansfor exciting and correcting the energization of the field of. thegenerator, 0 that the speed of the motor will be automatically heldaccurately at the desired value at all times, and also in order thatcertain desirable accelerating and decelerating characteristics may beobtained when starting and stopping the car.

The regulating means'includes the controlled main field winding RF forthe generator G which is designed to cooperate with the constantdifferential field winding GF to give the generator and the hoistingmotor the output characteristics desired.

We have further provided for controlling the main field RF by the use ofa pair of gaseous electronic discharge tubes 20 and 2|. The tube 20 isprovided with an anode 22, a grid 23, and a cathode 24. The tube 2| isprovided with an anode 25, a. grid 26, and a cathode 21. The cathodesmay be of the heated type and supplied with current from the secondarywinding 28a of a transformer 28 having a primary winding 29 connected toa suitable supply of alternating current represented by supplyconductors 30 and 3|, and an additional secondary winding 32. The anodesof the tubes are connected to the secondary winding 32. The terminals 33and 34 of the field winding RF are connected to the central portions ofthe secondary windings 32 and 28a.

It will be obvious that the current supplied by the tubes 20 and 2| tothe main field winding RF will control the energization of that fieldwinding and thereby control the energization of the generator GA. Theoutput of the tubes may be controlled by providing a means forcontrolling the energization of their grids 23 and 26.

The means for controlling the grids comprises a voltage tachometer orpilot generator PA designed to give an actual speed voltagecorresponding to the speed of the motor and an electronic tube 35 of thepentode type in conjunction with a capacitor or condenser 50 designed togive a pattern voltage for the desirable speedtime characteristic of theelevator for all load conditions.

The tachometer PA is mounted on and operated by the shaft H of thehoisting motor and it can be as small as is practical to build, sincethe current drain will be very minute. It should preferably have eitherpermanent magnet fields or regulated electromagnetic fields in order tomake the output voltage directly proportional to the speed of thehoisting motor and independent of all other variables, such astemperature or exciter voltage.

The pentode tube 35 comprises a plate or anode 36, a cathode 31, acontrol grid 38, a screen grid 39, and a suppressor grid 40. The cathode31 is provided with a filament heater 4| which is connected to thesecondary winding 42 of a transformer 43, the primary 44 of which isconnected to the alternating current supply conductors 30 and 3|. Thecathode 31 is connected by a tap 45 to a resistor 146, the outerterminals of which are connected to the direct current supply conductorsL+ and L. The screen grid 39 is connected to the resistor 146 by a tap39a at a point preferably about 20 to 50 volts positive with relation tothe tap 45. The suppressor grid 40 is connected to the cathode 31.

A pair of condensers 41 and 48 and an adjustable resistor 49 comprisinga variable time delay grid network are connected in the circuit of thegrid 38 with a bias tap 49a on the resistor r46 which is negative withrespect to tap 45.

The action of the time delay network in the grid circuit of tube 35 isas follows: (assuming the condition before the car starts) condenser 48has been charged to a negative potential which is beyond the value whichwould reduce the plate current of tube 35 to zero. When the car starts,or relay A picks up, condenser 48 is connected to the grid and at thesame time begins to discharge through theresistor 49. Thus, the gridpotential slowly changes from a value more negative than that whichwould cut on the plate current to the final grid potential determined bythe setting of the grid bias control on resistor r46. Thus, the platecurrent builds up relatively slowly. The time taken for this depends onthe time constant of the circuit 48, 49, which is proportional to theproduct of the'resistance and the capacity. Typical values are 1 mid.for condenser 48 and 1,000,000 or more for resistor 49.

The timing condenser 50, across which the pattern voltage is obtained,is connected in the circuit 500 of the anode plate 38. A pair ofcontacts M4 are disposed in the circuit 50a to assure that there is novoltage .on the condenser 50 before the car starts. (This is important.)A resistor 5| of low value (100 ohms maximum) is also associated withthe timing condenser 50 to prevent freezing of the contacts M4 shouldthey be closed when the condenser 50 is charged.

An adjustable resistor 52 is connected in the circuit leading from theplate 38 to the timing condenser 50 in order to produce a smoothtransition from the constant rate of increase of voltage to constantvoltage on the condenser 50. The action is as follows: the pentode tubehas the property of maintaining a constant plate current for a widerange of plate voltages except for voltages between 0 and about 25volts, where ,the value of the current is decreased. This results in anincrease in the time required to charge the condenser, being lengthenednear the fully charged point. (The voltage on the tube is the differencebetween the cathode tap to the contact Bl, tap 5B voltage and thevoltage existing on the condenser at any particular time.) Recognizingthen that the condenser current does not reach zero abruptly, it ispossible to make the transition from the constant current value(corresponding to the constant rate of build-up of voltage on condenserto zero current, longer in time by increasing the plate voltage at whichthe deviation from constant current takes place. This is done byinserting an additional voltage drop in the plate circuit, that acrossresistor 52 of the smooth transition from the cons'tant acceleration ordeceleration may be varied by changing. the value of the resistor 52.

The system also allows an adjustment of the running speed of the carwhich is very simple. The voltage at which the tap 56 for the contactsB4 is set determines the high speed of the car. Should any of the carsin a bank of elevators require lower speeds at certain periods of theday, this adjustment may be made with a simple, inexpensivepotentiometer. The voltage at which the tap 58 is set determines thepredetermined speed of the car for a one-floor run.

The pattern voltage conductor 53 leading from theplate 36 and the actualspeed voltage conductor 54 leading from the tachometer PA aredifferentially connected to the conductor 55 leading to the grids 23 and26.

A grid bias comprising a manually-set bias resistor 6|, a high valuecondenser 62 and a halfwave rectifier plate 63 are connected in serieswith the conductor 55 leading to the grids 23 and 26. Any suitablerectifier may be used. The loop circuit 64 extending through theresistor BI and the rectifier plate 83 is connected to the outer ends ofthe secondary winding 65 of a transformer 66, the primary 61 of which isconas a filter condenser to produce a substantially constant or puredirect current output voltage.

The pattern voltage and the actual speed voltage are differentiallyconnected so that the difierence voltage is connected in series with thebias 60 to the leads 2! and 26 of the two grid controlled gas rectifiertubes 20 and 2| which supply power to the main field winding RF of thegenerator.

The grid bias 60 is set so that the tubes 2|! and 2| are just preventedfrom conducting current when there is no pattern voltage. When the pattem voltage is started, the tubes 20 and 2| will fire, or conduct, aslong as there is a small difference between the pattern voltage and thespeed voltage. When the running voltage of the pattern circuit isreached, the tubes 20 and 2| will fire only often enough to maintain theelevator motor speed at the point where the actual speed voltageequals'the pattern voltage.

The method of controlling the grid rectifier tubes 20 and 2| may beapplied to single-phase half-wave or multi-phase half or full-waverectifier systems in a manner similar to that shown for single-phasefull wave.

Referring again to the differential field winding GF, this field isprovided with a weak constant energization in a direction to produce anopposite voltage to that of the main field winding RF. The purpose ofthis is to require the tubes to fire at intervals even at zeroexcitation. This permits a field forcing toward zero excitation thatwould not exist otherwise as it is possible to get only a one directionfiow of current from tubes. If no constant differential field wereprovided, the tubes 20 and 2|, at low motor speeds (corresponding to lowgenerator output voltages), would not be required to fire often tomaintain the generator field flux, thus causing the voltage output tofluctuate badly. With the addition of the differential field winding GF,the tubes are required to fire more often and thus reduce thefluctuation. field winding is of such strength as to overcome theresidual voltage of the field structure when a stop is made. Thereduction in fluctuation and the overcoming of the residual voltageincrease the reliability of the system at landing speeds. In practice,the strength of the diiierential field will preferably be made about 10%to 25% of the full field flux of the generator. It is then evident thatthe tubes will fire intermittently to maintain zero speed.

The transformers shown do not necessarily have to be separate, but allthe windings can be on one transformer. In normal use, the plate voltageand the filament voltage on the tubes 20 and 2| can be appliedsimultaneously since' the load circuit is not connected until the carnected across the alternating current supply constarts. However, inpractice; provision should be made to prevent the application of theload until the filaments are-thoroughly heated. Ordinarilya delay offrom /2 to 1 minute should be provided.

The operation of the system may be better understood from an' assumedoperation of the car. Assuming that the attendant on the car desires tomove it from one fioor to the next floor above, he throws the car switchCS into engagement with the contact CS2 for the up direction andimmediately returns the switch to its center position so that the carwill make the one floor run under-the most desirable conditions. Theengagement of the switch CS with the contact CS2 temporarily energizesthe up Also, the differential' direction relay UR and the car controlrelay R to start the car upwardly by the circuit:

L+, CS, CS2, UR, R, L-

The temporarily energized relay UR closes its contact members URI andthus energizes the up direction switch U and the car running relay M bythe circuit:

L+, URI, DRI, D3, SLU, U, M, L-

The energized relay M opens its contact members Ml, M2 and M4 and closesits contacts M3 and M to condition the car circuits for operation. Theclosing of the contacts M3 energizes the brake coil I1 to release thebrake IS. The opening of the contacts MI and M2 disconnects thedifferential generator field Winding GF' from the circuit of thearmature GA.

The opening of the contacts M4 allows the pattern or timing condensercircuit to become ready for operation.

The closing of the contacts M5 prepares a circuit for the relay Q.

The energized switch U closes its contacts Ul, U2, U3, U4, U6, U1, U8,U9, UN) and opens its contacts U5. The closed contacts U4 provide aself-holding circuit for the switch U and relay M.

The closing of the contacts UI and U2 energizes the generatordifferential field winding GF by the circuit:

L+, Ul, or, in, no, z

The closing of the contacts U3 and U6 prepares the main field winding RFfor operation in moving the car upwardly.

The closing of the contact members U1 and U8 prepares the tachometer PAfor operation in connection with moving the car upwardly.

The closing of the contacts U9 energizes the inductor control relay P toopen its contacts Pi to prevent operation of the stopping inductor relaySL until the car control system is conditioned to cause the car to makea stop. The circuit for the relay P extends L+, ISLU, U9, P, L

The closing of the contact members U9 also energizes the patternstarting relay A by the circuit:

L+, ISLU, U9, B2, A, L-

The energized relay A opens its contact members Al, A2, A4, A6, A8 andAll! and closes its contacts A3, A5, A1, A9 and All. The opening of thecontacts Al and A2 prepares the circuits of the inductor relays ISL andSL for operation under certain conditions.

The closing of the contacts A3 and A9 and the opening of the contacts A4and A8 reverse the connection of the condensers 41 and 46 and shortcircuit the resistor 49 in the time delay grid network for the cathode31 and the grid 38 to eifect the desired control of the pattern voltagecircuit. One pair of contacts of the relay A are arranged to allow onecondenser to be fully charged in the negative direction) before thestart of the accelerating period (or start of the car) and another pairare arranged to have the second condenser fully charged before the startof the retardation period, when it will discharge through the adjustableresistor 49.

The opening of the contact members A6 and All] and the closing of thecontact members A5 and All connect the pattern condenser 50 to the tube35 and thus allow the condenser to become charged at the rate determinedby the setting of the grid bias control and modified by the action ofthe time delay grid network. The firing of the tubes 20 and 2| andconsequently, the motor speed, then follows the pattern developed by thecondenser voltage.

The closing of the contacts Al completes a circuit for energizingtheinductor conditioning relay Q by the circuit:

L+, M5, m, Q, A1, L

The energized relay Q closes its self-holding contacts Q2 and closes itscontacts QI to energize the high speed inductor relay ESL and theintermediate speed inductor relay ISL for eiIecting the stopping of thecar at the next floor.

With this arrangement the pattern voltage from the condenser 50 operatesin conjunction with the voltage from the tachometer PA to so control thegrids 23 and 26 as to energize the main field winding RF in such mannerin comparison with the load on the car that the car will accelerate toits most desirable one-floor-run speed. (This is set by the position ofthe tap 58 for contacts B5 on the voltage divider resistance r46.)

The closing of the contacts UIO does not affect the pattern-circuitstarting relay A, because the contacts B3 of the time delay relay B donot close on account of the car switch CS being centered immediately foronly a one-floor run.

Returning now to the temporary energization of the relay R, that relaytemporarily opened its contacts RI and closed its contacts R2. However,its contacts R2 did not remain closed long enough to energize relay B toovercome its time delay. Therefore, relay B did not close itsselfholding contacts B6 and inasmuch as the contacts R2 reopenedinstantly, the relay B remains in its unenergized condition. In thiscondition, for a one-floor run, the contacts Bl remain open and thecontacts B5 remain closed, thus conditioning the circuit for the plate26 and condenser 50 for a one-floor run instead of for a run of morethan one floor.

Assume now that the car is continuing its movement toward the nextfloor. In doing so, it passes the intermediate speed inductor plate inthe hatchway for that floor (not shown) and thus operates the energizedinductor relay ISL to decelerate the car from its intermediate speed toits stopping speed. The operation of the inductor relay ISL opens itscontacts ISLU, thus deenergizing the relay P and the relay A.

The deenergized relay P closes its contact members Pi, thus preparingthe circuit of the stopping inductor relay SL for operation when the carcomes opposite the stopping plate for the floor. A

The deenergized relay A opens its con'tacts Al and A9 and closes itscontacts Al and A8 to connect the time delay grid circuit for theoathode 31 andthe grid 38 so as to prepare the pattern voltage circuitfor a decelerating pattern. The opening of the contacts A5 and All andthe closing of the back contact members A6 and Ali in the timingcondenser circuit condition that circuit to control the pattern voltageto effect deceleration of the car from intermediate speed to stoppingspeed.

When the contacts A8 and All! close, the condenser 50 is connected so asto discharge through the tube 35 (at the same rate as it had previouslybuilt up during the acceleration period). The differential connection ofthe condenser voltage and the tachometer or pilot generator voltage isnow such as to make the tubes 20 and 2| conduct or fire only oftenenough to cause the elevator motor to adhere to the pattern voltage andthe motor slows down.

In an extreme case, the tubes 20 and 2i could cease firing altogetherand so cause the rate of deceleration to be determined by the decay ofthe generator field flux through the parallel "rectox discharge unit 69.This is not the most desirable pattern, however, and it is mentioned asan example of the flexibility, of the system.

Assuming now that the car has decelerated to its stopping speed and hasalmost arrived at the next floor and that the inductor relay SL passesits inductor plate (not shown), then the relay SL is operated to openits up contacts SLU, thus deenergizing the up direction switch U and the'car running relay M, I

The deenergized relay M opens its contact members M3, thus applying thebrake Hi to stop and hold the car and also closes its contacts MI and M2to reconnect the' differential generator field winding GP to thearmature GA for the purpose of eliminating any residual magnetism in thefield as the stop is made. At the same time, the deenergized updirection switch U opens its contacts UI and U2, U3 and U6, and U1 andU8, thus deenergizing the generator field windings GF and RF and thetachometer PA. The deenergization of the gener-' ator field windings andthe application of the brake [6 stop the car level with the next floor.

The deenergization of the relay M also opens its contact members M torender the relays Q and B ineffective and closes its contact members M4to short circuit the timing condenser 50 through the resistor 5|, thusinsuring that the condenser 50 will have no charge when the car isstarted again;

Anwassumed operation of the car for a run of, more than one fioor is nowgiven. It will be assumed that the car attendant desires to make flan uprun of three floors and, therefore, moves the car switch CS intoengagement with the contact CS2 and maintains it in that position untilthe car approaches to within the stopping zone of that floor. Theclosing of the contacts CS2 energizes the up direction relay UR and thecar control relay R as previously described in the one floor operation.closes its contacts R2 and opens its contacts RI. The opening of thecontacts RI prevents energization of the inductor conditioning relay Quntil the car reaches the zone at which deceleration of the car for thenext fioor stop should start. The closing of the contacts R2 prepares acircuit for energizing the relay B.

The closing of the contacts URI of the up direction relay UR energizesthe up direction switch U and the car running relay M as previ- L+, M5,B, 32,1; v At the end of its time delay, the relay B will The energizedrelay R' k the timing condenser 50 to that portion of the resistor r48suitable for a more than one-floor run.

The energization of the up direction switch U also energizes theinductor control relay P and the pattern circuit starting relay A, aspreviously described. The relay A operates its contacts to connect thepattern tube 35 and the timing condenser 50 for operation as previouslydescribed, and the car starts to accelerate toward its normal highspeedoperation for a run of more than one fioor.

It will be assumed that the car, after arriving at its normal highspeed, continues toward the floor at which it is to stop, and that, asit approaches the zone in which it should be decelerated for the stop,the attendant centers the car switch CS. The centering of the car switchopens the contact CS2 and thus deenerglzes the up direction relay UR andthe relay ,R. The deenergized relay UR does not affect the circuit ofthe switch U, because of the self-holding contacts U4. However, thedeenergization of the relay R causes that relay to close its backcontacts RI, thus energizing the inductor control relay Q by thecircuit:

The energized relay Q closes its contact members Ql thus energizing thehigh speed inductor relay coil HSLto prepare it to efiect decelerationof the car from its normal high speed to its landing speed.

When the car nears the floor at which the stop is to be made, theenergized relay HSL passes its high speed inductor plate (not shown) forthat fioor and is thereby operated to open its up contacts HSLU, thusdeenergizing the pattern circuit relay A, to cause the car to.decelerate to its landing speed. This is effected because, as previouslydescribed the deenergized relay A opens its front contacts A3, A5, A1,A9, and All and closes its back contacts Al, A2, A4, A6, A8 and Alli.

When contacts A6 and AID close, the con-- denser 50 is connected so asto discharge through the tube 35 at the same rate as it had previouslybuilt up during the acceleration period. The differential connection ofthe condenser voltage and the tachometer or pilot generator voltage isnow such as to make the tubes 20 and 2| conduct or fire only oftenenough to cause the elevator motor to adhere to the pattern voltagewhich causes the motor to slow down.

The closing of the contacts Al' energizes the intermediate speed relayISL and prepares it for operation.

As the car continues on toward the floor, the inductor relay ISL comesopposite its inductor plate' (notshown) for that floor and is therebyoperated to open its contacts ISLU, thus deenergizing the relay P. Therelay P now closes its back contacts Pl, thus energizing the stoppinginductor relay SL to stop the car. It may be noted here that in thissimplified example of an operative system, the car is deceleratedcontinuously from its high speed to its landing speed at the end of amore than one-floor run by the operation of the high speed relay HSL,and, when making only a one-floor run, it is decelerated from the highspeed for that run to its landing speed by the action of theintermediate speed relay ISL.

As the car comes closer to the floor level at which the stop. is beingmade, the stopping inductor relay SL comes opposite its stopp g inductorplate (not shown) for that floor and is thereupon actuated to open itscontacts SLU, thus deenergizing the up direction switch U and the carrunning relay -M which, in turn, effect the stopp g of the car levelwith the floor and apply the brake to hold it there, as previouslydescribed in the operation of the one-floor run.

By the foregoing assumed operation, it will be understood that we haveprovided a control system which will automatically maintain a motor at-asubstantially constant predetermined speed regardless of load, and thatthe system will automatically accelerate and decelerate the motor in apredetermined manner in order to secure the most favorable results inoperating the motor while it is loaded.

It will also be apparent that our system is so fiexible that it may beeasily adjusted to suit various operating conditions because theconstant acceleration and constant deceleration, the amount of smoothtransition into and from constant acceleration and constantdeceleration, and the running speed, may be quickly and convenientlyadjusted to secure the desired values.

It will be apparent further that this variable voltage system controlledby the gaseous electronic discharge tubes might be readily used tocontrol the acceleration, deceleration, and regulation of motors inother applications where the characteristics previously described aredesirable,

Although we have illustrated and described only one specific embodimentof our invention, it is to be understood that many changes therein andmodifications thereof may be made without departing from the spirit andscope of the invention.

We claim as our invention: P

l. A variable voltage system comprising a power generator. having anarmature and a main field winding, a motor connected in a loop circuitwith said armature, a regulating gaseous elec-- tronic discharge tubeconnected to a source of energy for energizing the main field winding,said tube having a grid by means of which its output may be controlled,a voltage tachometer connected to the motor for providing a voltagecorresponding to the speed of the motor, an electronic tube and acondenser connected to a source of energy for providing a patternvoltage, manually operative means for controlling the pattern voltagetube, and means for differentially connecting the tachometer voltage andthe pattern voltage from the condenser to the grid of the regulatingtube for controlling the energization of the main field winding tomaintain the motor at a selected speed regardless of load.

2. A variable voltage system comprising a power generator having anarmature and a main field winding; a motor connected in a loop circuitwith said armature, a regulating gaseous electronic discharge tubeconnected to a source of energy for energizing the main field winding,said tube having a grid by means of which its output may be controlled,a voltage tachometer connected to the motor for providing a voltagecorresponding to the speed of the motor, an electronic pattern tube anda timing condenser connected to a source of energy for providing apattern voltage, manually operative means for controlling the patternvoltage. tube, means for differentially connecting the tachometervoltage and the pattern voltage from the condenser to the grid of theregulating tube for controlling the energization of the main fieldwinding to maintain the motor at a selected speed regardless of load,and a variable resistance-capacitance time delay circuit included in thegrid circuit of the pattern tube for building up the plate current onthe pattern tube to its constant value relatively slowly.

3. A variable voltage system comprising a power generator having anarmature and a main field winding; a motor connected in a loop circuitwith said armature, a regulating gaseous electronic discharge tubeconnected to a source of energy for energizing the main field winding,said tube having a grid by means of which its output may be controlled,a voltage tachometer connected to the motor for providing a voltagecorresponding to the speed of the motor, an electronic pattern tube anda timing condenser connected to a source of energy for providing apattern voltage manually operative means for controlling the patternvoltage tube, a circuit for differentially connecting the tachometervoltage and the pattern voltage from the condenser to the grid of theregulating tube for controlling the energization of the main fieldwinding to maintain the motor at a selected speed regardless of load,and a negative bias circuit disposed in series with said differentialcircuit.

4. A variable voltage system comprising a power generator having anarmature and a main field winding; a motor connected in a loop circuitwith said armature, a regulating gaseous electronic discharge tubeconnected to a source of energy for energizing the main field winding,said tube having a grid by means of which its output may be controlled,a voltage tachometer connected to the motor for providing a voltagecorresponding to the speed of the motor, a pentode tube and a condenserconnected to a source of energy for providing a pattern voltage,

manually operative means for controlling the pattern voltage tube, meansfor differentially connecting the tachometer voltage and the patternvoltage from the condenser to the grid of the regulating tube forcontrolling the energization of the main field winding to maintain themotor at a selected speed regardless of load, and an adjustable resistorconnected between the pentode tube and the timing condenser to produce asmooth transition from the constant rate of increase of voltage toconstant voltage on the condenser.

5. A variable voltage system comprising a power generator having'anarmature and a main field winding; a motor connected in a loop circuitwith said armature for operating an elevator car, a regulating gaseouselectronic discharge device connected to a source of energy forenergizing the main field winding, said device having a grid by means ofwhich its output may be controlled, a voltage tachometer connected tothe motor for'providing a voltage corresponding to the speed of themotor, an electronic tube and a timing condenser connected to a sourceof energy for providing a pattern voltage, means for diflerentiallyconnecting the tachometer voltage and the pattern voltage from thecondenser to the grid of the electronic discharge device for controllingthe energization of the main field winding to maintain the motor at aselected speed regardless of load; a control system for connecting thecircuits or the tube, the device, the timing condenser and the fieldwinding for accelerating, running and stopping the car; and meansresponsive to operation of the control system to stop the car forshort-circuiting the timing condenser while the car is stopped.

6. A variable voltage system comprising a power generator having anarmature and a main field winding, a motor connected in a loop circuitwith said armature, an electronic device for teeding the main fieldwinding, said device having a grid by means of which its output may becontrolled, a voltage tachometer connected to the motor for providing avoltage corresponding to the speed of the motor, an electronic tube anda timing condenser connected to a source of energy for providing apattern voltage, means for differentially connecting the tachometervoltage and the pattern voltage to the grid of the electronic device,for controlling the energization of the main field winding to maintainthe motor at a selected speed regardless of load, and a difi'erentialfield winding connected to a constant source of electric energy inopposition to the main field winding of the generator for bucking thefiuk generated by the main field winding for maintaining the electronicdevice conducting.

7. A variable voltage system comprising a power generator having anarmature and a main field winding, a motor connected in a loop circultwith said armature, an electronic device for feeding the main fieldwinding, and'a diflerential field winding connected to a constant sourceof electric energy in opposition to the main field winding formaintaining the electronic device conductive over the operating rangeofthe generator..

8. A variable voltage system for operating an elevator car comprising agenerator having an armature and a main field winding, a motor connectedin a loop circuit with said armature, a regulating gaseous electronicdischarge tube for energizing the main field winding, said tube having agrid by which its output may be controlled, a voltage tachometerconnected to the motor for providing a voltage corresponding to thespeed of the motor, an electronic tube and a timing condenser connectedto a source of energy for providing a pattern voltage, a car switch forcon trolling the pattern voltage tube and condenser, means fordifferentially connecting the tachometer voltage and the pattern voltagefrom the condenser to the grid of the regulating tube for controllingthe energization of the main field winding, and means responsive tomovement of is the car switch to its on" positio for only apredetermined time to connect the condenser to one point of potential onits source of supply 10 to cause the motor to accelerate to apredetermined speed for a one-floor run and responsive to maintainingthe car switch in its on position for a longer predetermined time forconnecting the timing condenser another point of potential on its sourceof supply to cause the motor to accelerate to a higher speed for a morethan onefioor run.

9. In a control system, a generator having an armature and a fieldwinding, means tor connecting the field winding to a source of electricenergy, a motor connected in a loop circuit with said armature, meansfor providing a voltage corresponding to the speed of the motor, meansfor providing a pattern voltage, said means comprising a condenser, aresistor and an electronic tube for charging the condenser through theresistor, means responsive to the difierence of the speed responsivevoltage and the pattern voltage for controlling the energy supplied tothe field winding, and a timed means for altering the rate oi! chargingsaid condenser at its extremities. 10. In a control system, a generatorhaving an armature and a field winding, means for connecting the fieldwinding to a source of electric energy, a motor connected in a loopcircuit with said armature, a tachometer generator for providing avoltage corresponding to the'spe'ed of the motor, an electronic meansfor providing a pat-- tern voltage, and means responsive to the diner-40 ence of the tachometer generator voltage and the pattern voltage foralteringthe energy supplied to the field winding to thereby reduce saiddifference in voltage to a minimum.

PAUL M. MARTIN.

ALVIN 0. LUND.

